Pump power governor

ABSTRACT

A device for governing the power of a pump has a conventional system for varying its cylinder capacity and a control arrangement therefor including linked members indicative of the pump delivery rate and the pump output pressure and regulator operable by said linked members to deliver the output of an auxiliary pump to one or the other chamber of a double acting ram of the control system if the linked members indicate that an increase or decrease in power is necessary or to a reservoir if the linked members indicate that the power is correct.

United States Patent 1191 Jan. 21, 1975 Pinson [5 PUMP POWER GOVERNOR3,669,570 6/1972 Himmler 417 222 3,732,036 5/1973 Busbey et al. [75]memo Claude senhs France 3,758,235 9/1973 Breeden 417/222 [73] Assignee:Societe Anonyme Poclain, Oise, 3,788,731 l/1974 Van Der Kolk 417/213France Primary ExaminerWilliam L. Freeh [22] Flled' 1973 AssistantExaminerGregory Paul LaPointe [21] Appl. No.: 384,789 Attorney, Agent,or FirmLewis H. Eslinger; Alvin Sinderbrand [30] Foreign ApplicationPriority Data Aug. 4, 1972 France 72.28292 [57] ABSTRACT Apr. 19, 1973France 73.14433 A device for governing the power of a pump has aconventional system for varying its cylinder capacity Cl 0/450 and acontrol arrangement therefor including linked [51] Int. Cl F04b 49/00members indicative of the pump delivery rate and the Field Of Searchpump output pressure and regulator operable by said 7/ 4 linked membersto deliver the output of an auxiliary pump to one or the other chamberof a double acting [56] References Cited ram of the control system ifthe linked members indi- UNITED STATES PATENTS cate that an increase ordecrease in power is necessary 2,932,984 4/1960 Neff et a] 417/222 toresermir if the linked members indicate that 2,971,498 2/1961 Bloch417/222 the Power 18 Correct- 3,l63,l15 12/1964 Neff et al 417/2223,554,671 1/1971 Schlinke 417/222 10 5 Draw": F'gures PATENTEU JANE 1I975 SHEET 2 OF 5 PATENTED I $861,832

SHEET 5 OF 5 PUMP POWER GOVERNOR The present invention relates to adevice for governing the power of a pump of variable cylinder capacity.

The power of a hydraulic or pneumatic pump is determined from theproduct of the flow delivery rate from the pump and the pressure of thefluid delivered. Once this product has been determined it is necessaryto keep it constant by governing the pump operation to follow ahyperbolic curve which determines the variation of one factor as afunction of the variation of the other.

In that case operation is generally by approximately by comparison ofportions of linearly varying curves which offer disadvantages.

The invention proposes to cure this complexity and these disadvantagesby a governor device which is simple to put into effect and precise inits results.

The object of the invention therefore is to provide a device forgoverning the power of a pump comprising particularly a system forcontrolling the variation of the cylinder capacity of the pump and adelivery pipe which consists of a first control member movable along afirst rectilinear guide, the displacement of which varies in proportionto the value of the flow rate of the fluid conveyed by the deliverypipe, and a second control member movable along a second rectilinearguide, the displacement of which varies in direct ratio with the valueof the pressure in the delivery pipe. A connecting rod of variablelength links the first and second members and passes through a fixed orpredetermined pivot point located at the intersection between twostraight lines each of which is drawn perpendicular to each of therectilinear guides from the position of each of the first and secondmembers signifying zero rate of flow or pressure. This fixed pivot pointis connected to the tip of the slide of a regulator valve in itsposition or rest connected with the connecting rod. When thedisplacement of the connecting rod with respect to the fixed point isrepresentative of an increase in power the regulator places an auxiliarypump selectively in communication with a first chamber of a doubleacting piston cylinder unit, the rod of the piston being linked to thecontrol system. When the displacement of the connecting rod with respectto the fixed point is representative of a drop in power the regulatorplaces the auxiliary pump in communication with the second chamber ofthe piston cylinder unit. When the displacement of the connecting rod iszero with resepct to the fixed point, the auxiliary pump is connected toa fluid reservoir.

In one embodiment the second control member aforesaid consists of apiston-cylinder unit having a fixed piston which constitutes the secondrectilinear guide for the cylinder mounted slidingly on this guide anddefines, with the said cylinder, a chamber connected to an exhaust pipe.Resilient means linked be tween the piston and the cylinder tend to makethe volume of the chamber a minimum.

The first control member consists of a movable cylinder mountedslidingly on a fixed piston which constitutes the first guide anddefines in the cylinder two chambers connected to the delivery pipe forthe pump on opposite sides of a restriction in the pipe. A resilientmember linked between the piston and the cylinder tends to make thevolume of the chamber connected to the delivery pipe between the pumpand the restriction a minimum.

Advantageously the restriction in the last mentioned pipe is formed by ahollow conduit in the piston actuator rod of the first control memberwhich has a gauge internal diameter and is arranged in series with theexhaust pipe.

The hollow actuator rod is slidably connected to the delivery pipe ofthe pump at the end thereof nearer to the pump. The other end of the rodis anchored in a fixed position and the rod is formed from a materialwhich has linear expansion characteristics compatible with the effectsof the temperature on the viscosity of the fluid so as to compensate fortemperature variatrons.

In a variant embodiment, the first control member is formed by the tipof the system of control of the variation of the cylinder capacity ofthe pump retained slidingly in a slide extending parallel with the axisof the pump, onto which tip is linked one of the tips of the connectingrod aforesaid.

Finally the connecting rod is preferably linked to at least one of thefirst and second control members aforesaid by means of an arm formedintegrally with the said member which arm extends perpendicular to theguide of the member and bears an adjustable member which forms the pointof attachment of the corresponding tip of the connecting rod.

The invention will be better understood in the course of the descriptiongiven below by way of purely indicative example which will enable theadvantage and secondary characteristics to be made clear:

FIG. 1 is a diagrammatic representation of a first embodiment of adevice in accordance with the invention;

FIG. 2 is a diagrammatic representation of a second embodiment of adevice in accordance with the invention;

FIGS. 3 and 4 are two respective variants upon the embodiments of FIGS.1 and 2;

FIG. 5 is a diagrammatic representation of a third embodiment of theinvention.

Referring to FIG. 1, there is seen a device for governing the power of apump 7 comprising a device for controlling the variation in its cylindercapacity 8 and a delivery pipe 9. This device comprises a first controlmember sensitive to the variations of flow from the pump 7, consistingof a movable cylinder 10 containing and slidably receiving piston 11having a rod 12 which constitutes a straight line guide for thecylinder. The piston 11 divides cylinder 10 into two chambers 13 and 14,respectively connected to pipe 9 by two pipes or conduits 15 and 16respectively formed on opposite sides of piston 11 in piston rod 12. Thelatter also includes a restriction 9a in communication with pipe 9 asseen in FIG. 1 and which is gauged in diameter and length such that theflow of fluid in restriction 9a is always laminar whatever its rate offlow. In the chamber 14 of cylinder 10 a spring 17 is positioned betweenpiston l1 and the end of cylinder 10 in such a way that its effect tendsto make the volume of the opposite chamber 13 a minimum.

A second cylinder 21 contains a piston 22 that divides the cylinder intotwo chambers with the chamber 24 thereof communicating with pipe 9through a port 25 formed in the fixed piston rod 23, which acts as aguide for this cylinder. Cylinder 21 is provided with a stud 27, havinga position indicated at 27' which signifies zero pressure in pipe 9.This stud is located in one of the slots 28 in a connecting rod 29,while a second slot 31 is arranged in connecting rod 29 so as to enablea pin 32 carried by the cylinder to slide along the connecting rod 29.The pin 32 adopts at the very least, theoretically when the flow fromthe pump 7 is zero, the position as indicated at 32'.

Two straight lines drawn perpendicular to the guides 12 and 23 from thepoints 27 and 32' meet at a predetermined point 34. The connecting rod29 passes through the point 34 when the device is in equilibrium asshown. At the equilibrium position the tip or free end of the rod 35which is pivotally connected to rod 29 is located at point 34. The rod35 controls the position of the slide of a regulator or valve 36 in theneutral position. The end of rod 35 is connected with connecting rod 29by means of a hingepin or the like in any convenient manner. Regulator36 is capable of putting an auxiliary pump 37 selectively incommunication with: (1) a pipe 38 connecting it to a first chamber 39 ofa doubleacting piston-cylinder unit 40; (2) with a pipe 42 connecting itto a second chamber 42 of the said unit 40; or (3) with a fluidreservoir 43 by means of pipeline 44. The rod 40a of the piston of theunit 40 is linked to the member 8 for controlling the variation of thecylinder capacity of the pump 7.

In operation the cylinders 10 and 21 have divergent movements when thedevice records an increase of pressure and an increase of flowsimultaneously. Recording of the variation in flow is effected by meansof a pressure take-off at each end of the restriction or gauge pipe 9a.In fact the flow of the fluid being laminar in this pipe 9a anyvariation in the rate of flow brings about a variation in load lossproportional to the variation in the rate of flow. This load loss in thepipe 9a creates a drop in pressure in fluid downstream of the pipe 911with respect to the fluid located upstream. The pressure in the fluidupstream of the pipe 9a is the pressure in chamber 10 since the latteris connected to the portion of the pipe 9 upstream of the pipe 9athrough the pipe or port 15.

The pressure in the fluid downstream of the pipe 9a is transmitted intochamber 14 of cylinder 10 through pipe 16. During flow of fluid in thepipe 9a the pressure in chamber 13 is always higher than the pressure inchamber 14. Equilibrium is achieved because of spring 17 which adds itsforce to that of the pressure in chamber 14. The result is that thegreater the difference in chambers 13 and 14, the greater thecompression of the spring 17, hence the greater the displacement ofcylinder 10 with respect to the fixed position 11. This difference inpressure is proportional to the rate of flow and hence the position ofequilibrium of the cylinder 10 and the compression of the spring 17 arerepresentative of this rate of flow.

Similarly, recording of the pressure in pipe 9 is achieved by means ofcylinder 21. The pressure in chamber 24 of that cylinder is the same asthat in the pipe 9 to which the chamber is connected through the pipe orconduit 25. The spring 26 balances the effect of the pressure in thechamber 24 and the position of equilibrium attained by the cylinder 21with respect to the fixed piston 22 results from greater or lesscompression of the spring 26, proportional to the value of the pressurerecorded.

The device described is indeed a governor of the power of a pump. It isknown in fact that the power of a pump is equal to the product of itsrate of flow and the pressure of the fluid discharged. If the distance32' 34 is called a, the distance 34 27' b, the distance 27 27 p (becauseit is significant of the pressure reigning in the pipe), and finally thedistance 32' 32 q, one can write from the fact that the device is inequilibrium and hence that the connecting rod 29 passes through thepoint 34:

by comparing the two triangles 32 32 34 and 27 27' 34 which are similarwhence the power W of the pump: W= p X q a X b. Whatever the values ofpand q this relationship will always hold if the connecting rod 29 passesthrough the point 34.

The governing principle therefore rests in the fact that the variationin the cylinder capacity of the pump must be subjected to the variationin the position of the connecting rod with respect to the predeterminedpoint 34 and that this variation in cylinder capacity brings about inreturn, by the action of the member 10, the location of the connectingrod 29 straight through the point 34. The subjection is then in a closedloop. Any variation of one or both of the values of the pressure and therate of flow of the fluid delivered by the pump 7 will modify theposition of the pin carried by or received in the connecting rod. Thisvariation will be communicated to the slide of the regulator 36 whichwill establish a communication between the auxiliary pump 37 and one ofthe chambers 39 or 42 so as to displace the rod 40a of the unit 40 andthereby actuate the member 8 for controlling variation of the cylindercapacity of the pump 7 in the direction of a compensation of thevariation of the pressures or rate of flow. if, for example, the rate offlow drops the connecting rod will change position and drive the slideof the regulator 36 into its position of putting the pump 37 incommunication with the pipe 38 and the chamber 39, bringing about byfilling of this chamber, a displacement of the rod 40a, and hence of thecontrol member 8, in the direction of increasing the cylinder capacity.Naturally any feeding of a chamber by the pump 37 opens the otherchamber to the exhaust in the convention manner.

IN FIG. 2 another embodiment of the invention is illustrated in whichcertain members described in relation to FIG. 1 are identified with thesame references. The pump 7 is represented in the form of a barrel pumpcapable of being driven in rotation by a shaft 52.

In a manner in itself known the pump includes rotary pistons havingpiston rods 53 maintained constantly in contact with a tiltable disc orplate 54 which is part of the system of controlling the variation of thepumps cylinder capacity, as by feeding fluid under pressure into pipe 9.The plate 54 is titltable (i.e., pivotable) on the axis or pivot 54a andis extended by a connecting rod 54b of variable length. This is achievedby use of a telescopic rod, without departing from the scope of theinvention.

Pipe 9 is in communication with the pipe 25 of cylinder 21 in order toconvey fluid at the discharge pressure from the pump into the chamber 24of the second member in the manner described above with respect to H0.1.

Connecting rod 29 is of variable length, and is linked between cylinder21 and connecting rod 54b by means of an idler stud 55 slidably mountedin the slot 54c of the connecting rod 54b and the slot 31 of theconnecting rod 29 at their point of intersection. The stud is alsoslidably retained in a fixed slide or slot 56 which extends parallel tothe axis of the pump 7. When the device is in equilibrium the connectingrod 29 passes naturally through the point 34 which corresponds with theintersection between the straight line drawn perpendicular to the guide23 through the point 27 and the straight line drawn perpendicular to theslide 56 through the point 55' representative of the position adopted bythe idler stud 55 during zero flow from the pump 7.

Accordingly, it is apparent that in this embodiment of the invention,the movable member indicating rate of flow is the stud 55 actuated bythe plate 54 controlling the variation of the cylinder capacity of thepump 7. The distance 55 S5 likewise called q signifies the theoreticalrate of flow from the pump since this rate of flow in contrast to FIG. 1is not measured but proceeds from the geometrical data of the pump. Theprinciple and the method of subjection of the pump is identical withthat of the device described in relation to FIG. 1. It is seenparticularly here that the plate 54 or the system of control 8 isactuated by a lug 57 carried by the rod 40a of the jack 40 and engagedin the slot 54c in the connecting rod 54b.

It will be noted that the device as shown in FIG. 1 governs the outputpower of the pump since the values that it takes into account are thepressure and rate of flow of the fluid really delivered. On the otherhand the device as shown in FIG. 2 governs the input power of a pumpbecause it takes into account a theoretical rate of flow and henceneglects leakages of fluid at the level of the pump.

It is understood likewise that the devices as in FIGS. 1 and 2 enablegoverning of the power of a pump at its value W a X b.

It is of interest to be able to select different powers to which theoperation of a pump can be restricted. To do this it will be apparentthat it is necessary to intervene either in the dimensions a or b or inboth at once. FIGS. 3 and 4 show how one can in a simple manner act upondimension a. It is quite obvious that these are only embodiments andthat numerous variants can be applied to them.

FIG. 3 takes up again in an arrangement similar to that of FIG. 1certain members from the latter with the same references. It is to beobserved that the cylinder includes an arm I8 having a slot 19 in whichis mounted slidingly the pin 32. The latter through a clamping device 33or the like is capable of being clamped or fixed in any position alongarm 13. Thus it will be seen that the movements of the cylinder 10 aretransmitted to the pin 32 which in turn is displaced along an imaginaryrectilinear guide symbolized by the line 12. The distance a to be takeninto account is hence that which separates the point 34 from this guide12'. By displacing the pin 32 along the arm 18 one chooses a and hencethe value of the power at which it is desired to govern the operation ofthe pump.

FIG. 4 shows a governor device similar to that of FIG. 3 with the samereference numerals applied to like ports, and has the possibility ofselecting the power of the pump. In order to do this the slide 56 isarranged in a guide 59. Under the effect of any sort of system ofcontrol a screw-andmut system, for example the position of the slide 56with respect to the guide 57 is acted upon. The dimension a is chosenand hence the power of the pump can be adjusted as described above.

It must however be pointed out that the dimension q is onlyrepresentative of the theoretical rate of flow from the pump if it istaken at a fixed distance from the axis of tilt 54a of the plate 54. Itis therefore necessary to arrange, between the slide 56 and theconnecting rod 54b linked to the plate 54, and auxiliary connecting rod58 furnished with a slot 580. The length q is then measured at the levelof the rod 40a of the jack 40 fixed with respect to the pump and theconnecting rod 58 capable of being displaced parallel to itself underthe action of the jack 40 recalls this length q to the level of themovable slide 54.

In the two embodiments as in FIGS. 3 and 4 it can be imagined thateither the part 32 of the slide 56 is subjected in position along itsguide to the power of another pump. The device in accordance with theinvention, due to this possible subjection, enables governing of thepower of a group of pumps comprising for example a constant flow pumpand a variable flow pump such as 7. The power of the constant flow pumpbeing only a function of the pressure of the fluid delivered, it issufficient to subject the slide 55 or the pin 32 to the pressure in theload circuit by means of a guide member of piston-cylinder type 21-22,the displacement of which would be made compatible with those of themembers described in the device in accordance with the invention.

Finally, FIG. 5 is a variant upon the device described with respect toFIG. 1 with like parts bearing the same reference numerals. In this formthe two movable members or cylinders 10 and 21 are arranged alongparallel guides or piston rods 12 and 23. The relationship W a X b p X qrequires that in order to define similar triangles 32, 32', 34 and 27,27', 34, described above. the connecting rod 29 at its point coincidingwith the point 34 must form a right angle. More generally, if the twoguides aforesaid define any angle between them the connecting rod 29which connects the two movable members must form an angle the complementof the angle between these two guides for the relationship a X b X p X qto hold. The control of the pump is the same as in the cases ofpreceding figures, that is, in a closed loop between the slope of thecontrol system 8 and the position of the connecting rod 29 with respectto the point 34.

An advantageous secondary characteristic of the invention will beobserved. In fact, if one refers to FIGS. 1, 3 and 5 it is seen that theconnection of the portion of pipe contained between the pump 7 and theguide 12 for the movable member 10 to the portion 9a of this pipe insidethe guide 12 is slidable and enables the two portions to be movable withrespect to one another in the direction of their greater dimension. Thisarrangement therefore enables movement of the guide 12 and in particularallows its expansion in the direction of its length.

Furthermore as previously mentioned, the difference between thepressures in chambers 13 and 14 of the member 10 are representative ofthe load loss in the fluid in the pipe 9a and therefore of its rate offlow and its viscosity, the latter in general becoming lower withtemperature. In other words, a given position of equilibrium of themember 10 will signify a greater and greater rate of flow in proportionas the temperature of the fluid flowing in the pipe 9a rises.

It is therefore necessary to provide a correction of the position ofthis member 10 as a function of the temperature of the fluid. This iseffected by using the guide 12 of a material having expansioncharacteristics which are compatible with the effects of the temperatureupon the viscosity of the fluid. By this selection a reduction in theviscosity of the fluid and hence in the pressure difference between thechambers 13 and 14, and therefore a displacement of the point ofequilibrium of the member in the direction of a fall in the rate of flowwill be compensated by a longitudinal expansion of the guide or pistonrod 12, thus bringing about a modification of the position of the pointof equilibrium of the member 10 in the direction of an increase in therate of flow.

The device in accordance with the invention has the further advantage ofoffering a simple kinematic device in which the movable members varylinearly with the physical magnitudes which they represent. The resultis great ease of execution and easy initial adjustment.

For reasons of simplification in the explanation only one embodiment ofthe invention has been described above, namely, two cylinders movablerespectively on two fixed guide-pistons. It is quite obvious that theinvention is not limited to this embodiment but that all the variantswhich might be applied to it without departing from its scope or spiritof the invention, particularly for example the modification of makingthe cylinders fixed and pistons mounted slidingly in them movable.

I claim:

1. A device for governing the power of a pump having exhaust anddelivery pipes, said device including control means for varying thepumps cylinder capacity, said device comprising a first rectilinearguide, a first control member movably mounted on said guide, meansoperatively connecting said control member to said pump for displacingsaid control member with respect to said guide distances proportional tothe value of the rate of flow of the'fluid delivered by the pump; asecond rectilinear guide, a second control member movably mounted onsaid second guide, means operatively connecting said second controlmember to said pump for displacing said second control member withrespect to said second rectilinear guide distances which vary in directratio with the value of the pump delivery pressure; a connecting rod ofvariable length operatively connecting said first and second controlmembers; said connecting rod being located to pass, when the device isin equilibrium, through a predetermined point defined by theintersection between two straight lines respectively drawn perpendicularto each of said guides from the relative position from each of the firstand second control members, representative of zero rate of flow andpressure; a regulator valve having a slide including a free endoperatively connected to said link at a position located at saidpredetermined point when the device is in equilibrium, and an auxiliarypump; said regulator valve including means for placing said auxiliarypump in communication with:

a. a first chamber of a double acting piston cylinder unit having apiston rod operatively connected to the control means for varying pumpcylinder capacity when the connecting rod is displaced with respect tosaid predetermined point due to an increase in power of the pump;

b. a second chamber of said piston-cylinder unit, having a piston rodoperatively connected to the control means for varying pump displacementcapacity when the connecting rod is displaced with respect to saidpredetermined point due to a drop in power of the pump; and

c. a fluid reservoir when the displacement of the connecting rod is zerowith respect to the predetermined point, indicating that constant poweris being maintained by the pump.

2. A device as defined in claim 1 wherein said second control memberconsists of a piston-cylinder unit having a fixed piston which definessaid second rectilinear guide for the cylinder mounted slidinglythereon. said piston defining in said cylinder a chamber connected tosaid exhaust pipe; and resilient means in said cylinder connectedbetween the piston and the cylinder for making the volume of the chambera minimum.

3. A device as defined in claim 2 wherein said first control memberconsists of a movable cylinder mounted slidably on a fixed pistondefining said first guide and forming in said last mentioned cylindertwo chambers connected by a conduit having a restriction therein; andresilient means connected between the piston and cylinder for making thevolume of the chamber connected to said delivery pipe between the pumpand the restriction a minimum.

4. A device as defined in claim 3 wherein the restriction in said pipeis formed by a conduit formed in the actuator rod of the piston of thefirst control member, said conduit having a guaged internal diameter andarranged in series with an exhaust pipe.

5. A device as defined in claim 4 wherein said conduit is slidablyconnected to the delivery pipe of the pump, and said conduit is securedin a fixed position at its other end and is formed from a material whichhas linear expansion characteristics compatible with the effects oftemperature on the viscosity of the fluid so as to compensate fortemperature.

6. A device as in claim 1 wherein said first control member isoperatively connected to said control means for varying the cylindercapacity of the pump by means of a slide connection extending parallelto the axis of the pump to which said connecting rod is also operativelyconnected.

7. A device as defined in claim 1 wherein said connecting rod is linkedto at least one of the first and second control members by means of anarm formed integrally with its associated control member, which armextends perpendicularly to the associated guide of the latter andincludes means for adjustably securing one end of the connecting rodalong the arm.

8. A device as defined in claim 6 wherein said slide is slidably mountedin a guide part arranged perpendicularly to its greater dimension andprovided with means for fixing the slide in any of its positions; and anintermediate connecting rod of variable length arranged perpendicularlyto said slide and capable of being displaced parallel to itself definingthe linking of the connecting rod with the control system; and means forconnecting the connecting rod and the intermediate connecting rod in theslide, the connection between the intermediate connecting rod and thecontrol system being maintained in a fixed guide extending parallel withthe direction of the slide.

9. A device as defined in claim 1 wherein said connecting rod isrectilinear and said two guides extend perpendicular to each other.

10. A device as defined in claim 1 wherein said cylinders and guides arelocated at an angle relative to each other and said connecting rod isformed in the shape of a V, the apex of which passes through saidpredetermined point and the angle of which is the complement of theangle between the two guides.

1. A device for governing the power of a pump having exhaust anddelivery pipes, said device including control means foR varying thepump''s cylinder capacity, said device comprising a first rectilinearguide, a first control member movably mounted on said guide, meansoperatively connecting said control member to said pump for displacingsaid control member with respect to said guide distances proportional tothe value of the rate of flow of the fluid delivered by the pump; asecond rectilinear guide, a second control member movably mounted onsaid second guide, means operatively connecting said second controlmember to said pump for displacing said second control member withrespect to said second rectilinear guide distances which vary in directratio with the value of the pump delivery pressure; a connecting rod ofvariable length operatively connecting said first and second controlmembers; said connecting rod being located to pass, when the device isin equilibrium, through a predetermined point defined by theintersection between two straight lines respectively drawn perpendicularto each of said guides from the relative position from each of the firstand second control members, representative of zero rate of flow andpressure; a regulator valve having a slide including a free endoperatively connected to said link at a position located at saidpredetermined point when the device is in equilibrium, and an auxiliarypump; said regulator valve including means for placing said auxiliarypump in communication with: a. a first chamber of a double acting pistoncylinder unit having a piston rod operatively connected to the controlmeans for varying pump cylinder capacity when the connecting rod isdisplaced with respect to said predetermined point due to an increase inpower of the pump; b. a second chamber of said piston-cylinder unit,having a piston rod operatively connected to the control means forvarying pump displacement capacity when the connecting rod is displacedwith respect to said predetermined point due to a drop in power of thepump; and c. a fluid reservoir when the displacement of the connectingrod is zero with respect to the predetermined point, indicating thatconstant power is being maintained by the pump.
 2. A device as definedin claim 1 wherein said second control member consists of apiston-cylinder unit having a fixed piston which defines said secondrectilinear guide for the cylinder mounted slidingly thereon, saidpiston defining in said cylinder a chamber connected to said exhaustpipe; and resilient means in said cylinder connected between the pistonand the cylinder for making the volume of the chamber a minimum.
 3. Adevice as defined in claim 2 wherein said first control member consistsof a movable cylinder mounted slidably on a fixed piston defining saidfirst guide and forming in said last mentioned cylinder two chambersconnected by a conduit having a restriction therein; and resilient meansconnected between the piston and cylinder for making the volume of thechamber connected to said delivery pipe between the pump and therestriction a minimum.
 4. A device as defined in claim 3 wherein therestriction in said pipe is formed by a conduit formed in the actuatorrod of the piston of the first control member, said conduit having aguaged internal diameter and arranged in series with an exhaust pipe. 5.A device as defined in claim 4 wherein said conduit is slidablyconnected to the delivery pipe of the pump, and said conduit is securedin a fixed position at its other end and is formed from a material whichhas linear expansion characteristics compatible with the effects oftemperature on the viscosity of the fluid so as to compensate fortemperature.
 6. A device as in claim 1 wherein said first control memberis operatively connected to said control means for varying the cylindercapacity of the pump by means of a slide connection extending parallelto the axis of the pump to which said connecting rod is also operativelyconnected.
 7. A device as defined in claim 1 wherein said connecting rodis linked to at least one of the first and second control members bymeans of an arm formed integrally with its associated control member,which arm extends perpendicularly to the associated guide of the latterand includes means for adjustably securing one end of the connecting rodalong the arm.
 8. A device as defined in claim 6 wherein said slide isslidably mounted in a guide part arranged perpendicularly to its greaterdimension and provided with means for fixing the slide in any of itspositions; and an intermediate connecting rod of variable lengtharranged perpendicularly to said slide and capable of being displacedparallel to itself defining the linking of the connecting rod with thecontrol system; and means for connecting the connecting rod and theintermediate connecting rod in the slide, the connection between theintermediate connecting rod and the control system being maintained in afixed guide extending parallel with the direction of the slide.
 9. Adevice as defined in claim 1 wherein said connecting rod is rectilinearand said two guides extend perpendicular to each other.
 10. A device asdefined in claim 1 wherein said cylinders and guides are located at anangle relative to each other and said connecting rod is formed in theshape of a V, the apex of which passes through said predetermined pointand the angle of which is the complement of the angle between the twoguides.